Polymeric palladium-mediated carbene polymerization

摘要: A metalloenzyme-inspired polymeric palladium catalyst, which was prepared by self-assembly of a imidazole ligand with PdCl2, promoted carbene polymerization high catalytic activity and reusability. Besides the atactic polycarbethoxycarbene (PCEC), small amount stereoregular PCEC also obtained poly(imidazole-Pd)-mediated ethyl diazoacetate (EDA). This is first example that polycarbene in an isolated form palladium-initiating system, suggesting steric could affect insertion process. Detailed end group analyses on revealed chain initiation termination mechanisms. XPS oxidation state changes center exhibited PdII reduced to PdI, suggests intramolecular electron transfer process occurred during interaction EDA. Kinetic studies showed zero order kinetic dependent concentration EDA, indicates strong binding EDA catalyst preceding formation. With addition radical inhibitor, reaction rate found be greatly decreased. In presence spin trap, striking paramagnetic resonance (EPR) spectrum detected, involvement intermediates. DFT calculations proposed Pd-carbene species supported EPR analyses, assigned significant density carbene-carbon atom. Based these results, we unprecedented metal-carbene mechanism, occurs through stepwise migration afford polycarbenes.